It is desirable to adjust the air gap on a wheel brake in view of the brake lining wear that is always present, and changes in boundary conditions, for example the brake temperature. This applies in particular to an electrically motor-driven wheel brake system on motor vehicles, in which the wheel brakes are actuated by activating electric-motor brake positioners. In these braking systems the air gap must be adjusted actively, i.e., by activating the brake positioner. Electrically motor-driven wheel brakes for motor vehicles are known, for example from PCT Publication No. 94/24453, where the application force is generated by an electric motor. In an electrically controlled braking system, a requisite air gap (spacing between the brake lining and brake disk or drum) should be maintained in the unbraked state at all operating points.
Important factors regarding the air gap are on the one hand that a small air gap is desirable in order to minimize the time necessary for application of the brake linings, while on the other hand a larger air gap is necessary so that in the unbraked state, frictional losses do not occur between the brake disk and brake lining in any operating situation, even, for example, in the event of impact on the brake disk or, because of the elasticity of the suspension system (steering knuckles, etc.) on poor road surfaces.